Screening of glycan biomarkers for early detection of colorectal cancer based on novel isotope labeling relative quantitative method

Colorectal cancer (CRC) is a prevalent gastrointestinal malignancy. However, the lack of diagnostic accuracy of traditional clinical serum biomarkers carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9) results in patients being diagnosed at an advanced stage. Herein, we developed a novel method of ultrahigh-performance liquid chromatography coupled to quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS) for relative quantification based on the non-specific enzyme pronase E and an isotope mass spectrometry (MS) probe 3-benzoyl/(benzoyl-2,3,4,5,6-d5)-2-oxothiazolidine-4-carboxylic acid d0/d5-BOTC to screen novel glycan biomarkers. We applied the method in a cohort of 102 serum samples (including 51 healthy volunteers (HV), 26 stage II CRC, and 25 stage III CRC) and 90 tissue samples (including 45 paracancerous tissue and 45 cancerous tissue). Results revealed that the serum levels of H5N4F, H5N4F3SA, H4N5F1SA, and H5N4SA2 in CRC patients were significantly different from those in HV (<i>P</i> < 0.01). The area under the curve values of H5N4F, H5N4F3SA, and H4N5F1SA in serum samples were 0.77, 0.71, and 0.91, respectively. The clinical diagnostic accuracies of these glycans ranged from 65% to 91%, which were significantly higher than those of CEA. Additionally, differential glycan profiles in tissues were further examined using the same method and compared with serum levels. H5N4F was found to be significantly down-regulated in all CRC groups (<i>P</i> < 0.0001), indicating strong specificity for CRC diagnosis. The glycans identified in this study are expected to serve as potential biomarkers for the early diagnosis of CRC, offering valuable reference points for clinical diagnosis and treatment.